Copolyester elastomers are thermoplastic polymers which are easily processed but they lack the important physical characteristic of good compression set resistance found in vulcanized thermoset elastomers. Further, copolyester elastomers exhibit high permanent set values and a draw plateau when elongated.
There has been a need in the industry to develop a thermoplastic composition having improved compression set resistance so that the dimensions of an article of manufacture, for example, the thickness of seals, will be restored after pressure that has been applied is released. Also, multi-block copolyester elastomers are deficient in resistance to permanent set. It is important for the material to return to substantially its original form after deformation by extension. For some uses, for example, gaskets and seals, multi-block copolyester elastomers are harder than desirable and either cannot be used or they are limited in their uses for such applications. Multi-block copolyester elastomers are not especially scuff resistant and there is a need to improve this characteristic. Also, there is a need for elastomeric thermoplastic compositions which do not have the draw plateau that is observed for multi-block copolyester elastomers.
Although multi-block copolyester elastomers are not normally compounded with fillers and extenders, the thermoplastic elastomeric compositions of the present invention can accept substantial amounts of processing oils and/or fillers while still retaining good physical properties. The incorporation of fillers and/or extenders in the thermoplastic compositions of the present invention is beneficial because it lessens the cost of the polymers, makes processing easier and improves properties such as tear strength. The thermoplastic compositions of the present invention have good compression set resistance, improved resistance to permanent set relative to copolyester elastomers, they are scuff resistant and softer than copolyester elastomers. Further, the compositions show good resistance to oil swell and they can be readily processed by conventional means used for thermoplastic compositions.